This invention relates to an intravascular catheter assembly to be set in the blood vessel for the external blood circulation through a particular tube provided outside of the body of a patient or the administration of a medicinal liquid into his blood vessel.
An intravascular catheter is generally carried into the blood vessel with a cannula previously piercing the wall of the blood vessel used as a guide. If, in this case, the cannula is pulled out without applying any proper precautionary means after the insertion of the catheter into the blood vessel, the blood is liable to leak out through the catheter. To prevent this event, a thin-walled rubber cap has hitherto been fitted to the peripheral surface of the tubular hub of the conventional blood vessel catheter. The leakage of blood was prevented by piercing the cannula through the rubber cap.
Where, however, the intravascular catheter was assembled, the cannula was always made to pierce the rubber cap. Therefore, the sharp blade edge of the cannula was often damaged. Where the cannula was pushed through the wall of the blood vessel with the damaged blade edge of the cannula left intact, as is customarily the case, then there arose problems such as the increase of pain to a patient or injury to the blood vessel.
Further, the intravascular catheter was required to be fitted with, for example, another tubular member. In this case, the rubber cap fitted on the hub portion of the catheter with its flange turned back so as to prevent it from being removed at the time of the withdrawal of an inner needle had to be removed by being turned over, each time the tubular member was connected to the catheter. This removal operation was troublesome and time-consuming. Moreover, the rubber cap was not directly fitted around the hub of the catheter. Instead, the rubber cap was connected to the proximal end of the catheter hub with a flexible tube disposed between said rubber cap and catheter hub. Where, therefore, the cannula was pulled out of the rubber cap, the intervening flexible tube was undesirably elongated due to friction between the cannula and rubber cap, failing to ensure a safe operation.
Where the cannula was fitted to the catheter, the customary process of defining the position of the cannula so as to cause the distal end of the cannula to slightly protrude from the distal end of the catheter was (a) to form a stepped portion on the peripheral surface of the cannula and also a stepped portion on the inner wall of the hub and cause both stepped portions to engage each other, or (b) to provide one end of the cannula with a cylindrical portion capable of being fitted around the peripheral surface of the aforesaid intervening flexible tube, fit a bayonet prop to the proximal end of the cylindrical portion, provide bayonet pawls on the peripheral surface of the hub and cause the bayonet prop to be engaged with the bayonet pawls.
However, with the above-mentioned known cannula-locating process of forming a stepped portion on the peripheral surface of the cannula, the stepped portion of the cannula strikes against the stepped portion formed on the inner wall of the blood passage of the hub, tending to damage the stepped portion of the hub. Moreover, the blood is liable to be stagnantly gathered around the stepped portion of the hub in the vortical form, and consequently flow is retarded. This event sometimes gives rise to the coagulation of the blood. Further, the proximal end of the cannula which was provided with a stepped portion had a larger diameter than the distal end thereof, thereby resulting in an increase in the resistance which was applied to the removal of the rubber cap and consequently the greater elongation of the aforesaid flexible intervening tube.
With the prior art bayonet type cannula-locating process, the bayonet pawls protruding from the peripheral surface of the hub bite into the skin of, for example, a patient, when the catheter is fixed to his body, thus imparting unnecessary pains to him. Further drawbacks of this bayonet type cannula-locating process were that the cannula had to be rotated, each time it was taken into and out of the patient's body, tending to injure his blood vessel, and moreover, the insertion and removal of the cannula always involved complicated steps and consumed much time.